1. Field of the Invention
The present invention relates to a technique for designing a semiconductor integrated circuit. In particular, the invention relates to a technique for designing a semiconductor integrated circuit including dummy patterns.
2. Description of Related Art
If a semiconductor integrated circuit is designed, then areas having dense wiring patterns and areas having sparse wiring patterns may be generated therein. In other words, areas having high wiring pattern densities (hereafter referred to as a “pattern density”) and areas low wiring pattern densities may be generated. Such uneven pattern densities may cause various problems in the manufacturing process of a designed circuit.
For example, when a chemical mechanical polishing (CMP) process is performed, there occur differences in polishing characteristics between areas having high pattern densities and areas having low pattern densities. As a result, there occurs a phenomenon, called “dishing,” in which a surface of wiring (e.g., Cu wiring) is recessed in the form of a dish (e.g., a concavity). Dishing means a reduction in flatness of wiring and a reduction in film thickness and causes uneven wiring resistances and an increase in wiring resistance.
In order to suppress generation of such a defect in the manufacturing process, it is important to make pattern densities as uniform as possible in the stage of circuit design. For this reason, “dummy patterns” as well as wiring patterns (signal wiring, power supply lines, ground lines, etc.) of the circuit are generally added to a design layout (see Patent Documents 1 and 2). A dummy pattern is a wiring pattern unnecessary for functions of a designed circuit and is also called as dummy wiring or a dummy metal. Addition of dummy patterns makes pattern densities more uniform, thereby suppressing generation of dishing or the like.
Described in Patent Document 1 is a technique for improving local uniformity in wiring pattern. For that purpose, a layout area is divided into multiple division areas and a dummy pattern is inserted between designed patterns in each division area.
Described in Patent Document 2 is a method for forming a dummy pattern having highly uniform cover rates. According to this method, a dummy pattern formation area is divided into multiple dummy pattern formation unit areas. Subsequently, multiple check ranges having an area larger than the dummy pattern formation unit area are set. The multiple check ranges overlap each other. Subsequently, a temporary cover rate of a dummy pattern to be formed in a dummy pattern formation unit area in each check range is calculated. By averaging the calculated temporary cover rates, a final cover rate is determined. A dummy pattern having an area corresponding to the final cover rate is formed in each dummy pattern formation unit area.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-39951    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2006-60051
As described above, in order to improve the yield of a semiconductor integrated circuit, it is important to previously dispose a dummy pattern in the design stage. However, the time required to perform a dummy pattern disposition process is increased as the size of a designed circuit is increased. This increases the design TAT (turn around time). For this reason, it is considered to divide a layout area into multiple division areas and then perform dummy pattern disposition processes “simultaneously” with respect to the multiple division areas so as to reduce the design TAT.
Here, the inventor was focused on the following point. That is, if a layout area is divided carelessly and dummy pattern disposition processes are performed with respect to the multiple division areas separately, then the following problems may occur.
For example, a dummy pattern disposed in a division area may excessively come close to a wiring pattern in an adjacent division area. That is, a design rule error (spacing error) may occur between the patterns in the adjacent division areas. This is because dummy pattern disposition processes are performed on the division areas separately.
In order to stabilize the electric properties of a dummy pattern to reduce noise, it is desirable to couple a disposed dummy pattern to a power supply line or a ground line. Here, a case is considered where a first dummy pattern is disposed in a division area, a second dummy pattern is disposed in an adjacent division area, and the first and second dummy patterns are coupled to a power supply line and a ground line, respectively. In this case, it is considered that the first and second dummy patterns make contact with each other or overlap each other on the boundary between the division areas. Thus, a short circuit occurs between the first and second dummy patterns.